I carried out an experiment where I observed sporulation in a Bacillus species. The bacteria was innoculated in this medium that contained a bunch of salts, glucose, and ammonium acetate. Every few hours or so, we were required to take the pH of the sample.

My results: Between T = 0 to 8 hours, the pH decreased from about 7.4 to 6.8. We didn't measure it again until the next day (so a total of 28 hours passed initial inoculation) and the pH rose to 6.9. Then, another measurement was taken that day where it dropped to 6.8 again. According to my TA, this rise and drop should be observed.

The thing I don't quite understand is what pH should exactly tell us or how it would change during sporulation. I've looked up numerous articles, which all mainly focus on the EFFECT of changes in pH on sporulation, of which I do understand (eg. outside given preferred range => sporulation). However, we did NOT do ANYTHING to the mediums. They were only inoculated, left on a shaker, and samples. At no point were nutrients added/removed.

At first I thought maybe it had to do with lactic acid production if the thing is anaerobic...but I think my species is aerobic/facultative (commonly found in soil, actually). So I really doubt it would've produced any acid to result in that change in pH. But this was just a wild guess.

Ah, yes! I managed to find a few articles in regards to acetate production (or I guess acetic acid). Which would make sense, cause then it could go into the TCA cycle (where rise in pH likely occured).